Non-Polar or Bipolar Electrolytic Capacitor 4.7uF, 16V



Non-Polar and bipolar are both used to describe electrolytic capacitors which may have a voltage of either polarity applied.  In this particular case, the only indication that the capacitor is a bipolar type is the absence of a polarity marking.  Often there will be some other indication such as an "N.P." mark.  The schematic symbol is usually that of an ordinary capacitor.  These need to be used where you can't guarantee that the voltage on the capacitor will always be in the correct direction.  This is often due to there being a significant A.C. signal voltage present which inverts the polarity on the capacitor for some of the time.  That's despite there being a correct average D.C. bias on the cap, or when there is no signal present.  This is a very common mistake seen when normal electrolytic capacitors are used as a D.C. blocker in real hi-fi amps and old TV sets.  The capacitor dies, but only after a year or so, by which time you've manufactured thousands of units.

In the circuit, C8 is used to block the D.C. voltage between VR1 and the audio amplifier stages.  You can see that the D.C. voltages marked on the schematic diagram are very close on either side, so a non-polar type is called for.

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